Advancements in propulsion technologies have required gas turbine engines to operate at higher temperatures. This increase in operating temperature has required subsequent advancements in the operating temperatures of metal gas turbine engine components, such as superalloy turbine blades and vanes. To meet these requirements, thermal barrier coatings comprising alumina or zirconia based ceramics have provided an insulative layer protecting the superalloy substrate. To apply protective ceramic coatings, a superalloy substrate is first coated with a metallic bondcoat, such as a diffusion aluminide and/or MCrAlY overlay coating (where M is nickel and/or cobalt). This bondcoat is then coated with an insulative layer of alumina or stabilized zirconia.
During thermal barrier coating production and/or turbine engine component refurbishment, removal of the ceramic insulating layer may be necessary. Thermal barrier coatings traditionally have been removed by grit blasting, HF cleaning, water jet, or caustic autoclave chemical removal at high pressures and temperatures. These operations: are energy intensive, require long processing times, are labor intensive, damage underlying bondcoats, decrease component wall thickness, and increase surface film cooling hole sizes in multi-passage air-cooled component.
It is an object of the present invention to provide a method for removal of a thermal barrier coating rapidly and without damage to an underlying metallic substrate, such as a gas turbine engine component for example, or any bondcoat thereon.
It is another object of the present invention to provide a method for removal of a thermal barrier coating rapidly and without damage to an underlying metallic substrate or any bondcoat thereon using a hydroxide medium at ambient pressure and elevated temperature.
It is another object of the present invention to provide a thermal barrier recoated component that exhibits improved resistance to oxidation following removal of the used thermal barrier coating pursuant to the present invention and recoating with a fresh thermal barrier coating.